Electrical switches are used for switching electrical currents. One class of electrical switches is what are referred to as power circuit breakers, which can typically switch currents of 100 A and more. The power circuit breakers are typically accommodated in a housing.
The individual phases of the currents can be switched in what are referred to as pole cassettes. A pole cassette comprises a housing in which a movable and a fixed contact are accommodated, which can be mechanically separated or brought together for switching off for switching on the currents.
During separation under a current flow by movable and fixed contact of a pole cassette an arc is produced which is extinguished in an extinction chamber. The arc ionizes the gas of the extinction chamber and generates excess pressure in the extinction chamber which is equivalent to the arc energy. Power circuit breakers are also known which do not contain any pole cassettes but in which movable and fixed contact are shielded in some other way in their housing.
The housing of the electrical switch is typically constructed such that it can be closed off with a removable cover, the so-called accessory cover. Typically accessories are built into the housing of the electrical switch in the vicinity of a handle. The handle serves to manually switch the electrical switches between different states, for example switching them on or switching them off. In order to install or exchange the accessories the housing is provided with a removable accessory cover which can be easily opened or closed again by an installer. In the event of the short circuit switching off of the electrical switch the ionization of the gases of the extinction chamber by the arc cause high-pressures to be produced in the electrical switch. These high pressures can lead to the accessory cover being subjected to mechanical stresses or can even destroy the cover.